Fuel gauge level and reserve

M

MUNKSJOE

Member
Dear All,
Do not use my 3500 enough so the fuel gauge usually does not go below half, until yesterday. It registered just over one quarter full and the engine stopped. I pulled out the reserve control and after several turn overs the engine started again and behaved as usual.
I know that the tank capacity is 68 ltrs including 12 ltrs reserve but my question is, when should the fuel reserve come into play. I would have thought when the gauge was on empty and not just over one quarter full. Wanted to find out before I replace the sender unit which means covering myself with fuel and becoming a fire risk.
Any advise would be appreciated.
Regards
Alan
 
That's pretty normal as far as i know, the fuel indication is more exponential rather than linear.
Mine demands to use the reserve just below the last quarter, so i always think of the last "quarter" as reserve.
There's plenty of fuel at the top end though!
 
My gauge is pretty accurate, insofar as the amount needed to fill the tank is generally close to what is indicated on the gauge. I have to pull the reserve when the needle is just into the final segment (so just under a quarter of a tank) and it takes around twelve gallons to fill up.
 
I get around 220 miles from full to half then about 100 more from half to needing a fill-up. I only ever have to pull the reserve when the needle is almost at empty.

Dave
 
The accuracy of both the fuel and temperature gauge readings rely on an accurate output from the voltage regulator, mounted on the back of the combined fuel/temperature gauge unit.

This regulator uses the then-contemporary bi-metallic strip technology, similar to a flasher unit, and gives variations from car to car.

Not a problem at all, once you know how your car's gauges behave.

Whilst I'd got the gauges out, however, I replaced the original Lucas VR with a solid-state regulator which gives much more accurate readings. Available from Maplins for around a quid, and an easy fit. (Thanks, colnerov!).

The Maplin link's buried in this thread: http://www.classicroverforum.net/viewtopic.php?f=16&t=18406

Stan
 
Thank you to all for your helpful and informative replies.
As the tank holds 68ltrs and one quarter would be 17ltrs I guessed that If my gauge was reading one quarter and I filled the car with 17ltrs it should read half full. Well Bingo the needle sat bang on half after putting in the fuel. Obviously now this means that the sender is correct so I will not have to change it with the possibility of turning myself into a human fire ball. However, I do still wonder why as the good people on this forum have stated, different cars vary greatly on when to use the reserve. Are the senders that inaccurate or have I just got used to the modern digital technical thingies used today.
Again thanks to all for your help.
Regards
Alan
 
Hi, It doesn't matter how accurate or inaccurate the gauge is because you have the reserve.
Because once you pull it you know there is 12 litres left. If you don't respond to the grace it
gives you and put more in, that is your own fault. With an indicator light of low fuel you still
don't know how much there is left because you don't know how accurate it is.

Colin
 
Hi Coin,
I had never used the reserve and in fact have never had a car that has one in the guise of a lever. It was a shock to suddenly have the engine splutter for a short while and then stop completely. After looking at the gauge which was on just over a quarter of a tank (with no red mark to indicate reserve) a number of things came to mind one of which was fuel. Lever pulled, engine started all good to go. I now know when to pull the reserve but thank goodness I was not doing 70mph on the motorway.
Regards
Alan
 
MUNKSJOE said:
Hi Coin,
I had never used the reserve and in fact have never had a car that has one in the guise of a lever. It was a shock to suddenly have the engine splutter for a short while and then stop completely. After looking at the gauge which was on just over a quarter of a tank (with no red mark to indicate reserve) a number of things came to mind one of which was fuel. Lever pulled, engine started all good to go. I now know when to pull the reserve but thank goodness I was not doing 70mph on the motorway.
Regards
Alan
Click to expand...

I use my reserve for just about every tank fill the car gets, Its a great system.
Dont worry at 70MPH there is no drama, the car just starts to decelerate you reach down pull the lever and with in 2 to 3 seconds it all back again Zero drama.

Graeme
 
hi guys...great topic...hope it's ok if i 'hijack it'.

this afternoon i had to park by the side of the road as i wasn't getting any fuel to the carbs every time i and driving uphill. my fuel line is brand new and from the tank it goes straight to the electrical pump ,then filter and then carbs. My sender is probably faulty, as it only show much less than 1/4 even after I topped up full a month ago, so i never know how much fuel i really have left. today whilst on the motorway i had to nurse it ever so slowly to an exit where i can park safely. it was nerve wrecking as hell as auckland is full of crazy drivers. the car just loses power when it's coming up a slope, flat surface it runs well.

i am at a lost because i know i had topped up a lot of fuel a month ago and i don't think the car has been driven more than 100KM, so 68ltr can't just disappear. but i can't tell how much fuel there really is either. However the fuel filter looks dirty today which makes me suspect that it is sucking the last batch of fuel which is why when i drove uphill, the pump is struggling and you can hear it making loud machine gun noise. but this is all my assumption.

I am very tempted to save $100 on towing and and drive the rover back to my place myself tonight when there is no traffic. I hope just topping up 20ltr of fuel should do the trick but is there anything else i should look into before i drive off?

One question though, how much gunk can a car that has sat for 7yr can really have? (the car was sitting for 7yrs when i bought it) and how can i fix the float unit without taking the tank out or draining the fuel? and how can i clean the tank itself?

sad times ahead...
 
Could be many things, I would first think that the petrol tank is full of crud, lucky you have a fuel filter.
Putting more gas in will help to get it running, I wouldn't be pulling the reserve tank knob if its crud as the reserve tank is a lower point in the tank ie more crud.
I would be checking that there is not fuel leaking out of the carb seals, this can happen as the seals age and crack or other carb parts fail causing leaking, raw petrol onto the top of a hot engine, not a good look.
Check for fuel line leaks from all points in the fuel line, rubber ages and cracks, the plastic fuel lines whilst very durable have also been known to form splits. If the original mechanical fuel pump is still fitted check that for external leaks and check the engine oil for petrol as a mechanical fuel pump can leak into the sump if the diaphragm fails.
The reserve tap located on the drivers side next to the bell housing on the inner guard firewall area can also leak if the o-ring fails

Graeme
 
The facet electric pump has a strainer in one end that can fill with crud. There is also a tap to turnoff the supply so you can undo the end of the pump, remove and clean filter without draining tank though you can still get a bit smelly. I normally do this routine with the back of the car high and a low tank so the remaining fuel in the line is below the pump to prevent backflow.

Draining the tank on an electric pump car is relatively easy, you just need to replace the pumps output pipe with a nipple and pipe into a big enough drum, then turn the IGN on and wait till it pumps the tank dry. A one way valve between nipple and pipe is good to stop the fuel running back when you disconnect the pipe as most containers fill above pump level easily due to its low position.
 
I always try and keep my fuel tanks full . Especially my truck and tractor diesel tanks and esp over the winter months .
I do the same with my P6 too as it doesn't get the same amount of use.
My reason .
Fuel to the top stops Condensation build up on the inside of a half empty tank .
Condensation = water contamination and ultimately rust .
I was told this as a farm boy and somehow its stuck over my 50 years of playing/maintaining engines.
 
rafrover said:
hi guys...great topic...hope it's ok if i 'hijack it'.

this afternoon i had to park by the side of the road as i wasn't getting any fuel to the carbs every time i and driving uphill. my fuel line is brand new and from the tank it goes straight to the electrical pump ,then filter and then carbs. My sender is probably faulty, as it only show much less than 1/4 even after I topped up full a month ago, so i never know how much fuel i really have left. today whilst on the motorway i had to nurse it ever so slowly to an exit where i can park safely. it was nerve wrecking as hell as auckland is full of crazy drivers. the car just loses power when it's coming up a slope, flat surface it runs well.

i am at a lost because i know i had topped up a lot of fuel a month ago and i don't think the car has been driven more than 100KM, so 68ltr can't just disappear. but i can't tell how much fuel there really is either. However the fuel filter looks dirty today which makes me suspect that it is sucking the last batch of fuel which is why when i drove uphill, the pump is struggling and you can hear it making loud machine gun noise. but this is all my assumption.

I am very tempted to save $100 on towing and and drive the rover back to my place myself tonight when there is no traffic. I hope just topping up 20ltr of fuel should do the trick but is there anything else i should look into before i drive off?

One question though, how much gunk can a car that has sat for 7yr can really have? (the car was sitting for 7yrs when i bought it) and how can i fix the float unit without taking the tank out or draining the fuel? and how can i clean the tank itself?

sad times ahead...
Click to expand...

I'm having exactly the same problem with our P5B. The car sat for nearly 20 years so we flushed out the tank as best we could. After refilling and fitting an in-line fuel filter the problem developed. After the petrol level has dropped about 20 litres from full the engine cuts out and (after quite a bit of swearing) I have to top it up from our spare can. The reserve tap doesn't seem to make any difference but the engine eventually does start again and we can continue the journey. Luckily every time it has happened so far we have not been stuck in traffic or at busy intersections. Our luck may not hold out for much longer.

I discovered the fuel pick-up pipe in the tank has a fine mesh strainer on the end which was almost completely blocked. Carefully removed the deposit with a fine bronze brush and air jet, reassembled and thought "that will fix it". It hasn't!

I intend to check the fuel lines and connections for air leaks but after that the next step will be to remove and overhaul the mechanical fuel pump, hoping that it will suck a bit better. It's possible the diaphragm is suspect or the valves are leaking. I don't want to fit an electric pump, as I'd rather keep the old girl as original as possible.

Any other suggestions for things to look for would be very much appreciated.
 
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